1. Field of the Invention
The present invention relates to an optical recording medium having data recorded in the form of a train of pits, a master for use in production of the optical recording medium having data recorded in the form of a train of pits, and an optical recording/reproducing apparatus to write and/or read data to and/or from an optical recording medium having data recorded in the form of a train of pits.
2. Description of the Related Art
As a typical one of the optical recording media, an optical disc to and/or from which data is optically written and/or read, is well known. The optical disc includes a read-only type having data pre-recorded in the form of a train of pits, a magneto-optic type to and from which data is written and read using the magneto-optical effect, and a phase-change type to and from which data is written and read using a phase change of a recording layer thereof.
For these types of optical discs, it is very important that tracking servo and track seek can stably be done during data write and/or read. Note that the xe2x80x9ctracking servoxe2x80x9d is to have a light spot track a recording track. The xe2x80x9ctrack seekxe2x80x9d is to move the light spot to a desired recording track. For the track seek, it is necessary to count recording tracks the moving light spot has traversed until the light spot arrives at the desired recording track. This is generally called xe2x80x9ctraverse countxe2x80x9d.
Conventionally, the reading resolution of an optical pickup mounted in an optical recording/reproducing apparatus has been improved to attain a high density of recording in the conventional optical discs. For the conventional optical discs, a main measure taken to improve the reading resolution of the optical pickup is to use a laser light of a shorter wavelength xcex for reading data or an objective lens having a larger numerical aperture (NA) for focusing the laser light onto an optical disc.
The wavelength xcex of a laser light used to read data, numerical aperture (NA) of objective lens and track pitch will be shown in Table 1 concerning CD, MD, MD Data 2, DVD+RW and DVD-ROM as examples of tie optical disc.
As shown in Table 1, the conventional optical discs use a laser light of a shorter wavelength xcex or an objective lens having a larger NA to implement a narrow track, whereby a high recording density is attained.
Even with the narrow track for the conventional optical discs, however, the spatial frequency of the track pitch is limited to the order of a half to two/thirds of the cut-off frequency of the optical pickup of the optical recording/reproducing apparatus. Note that the xe2x80x9ccut-off frequencyxe2x80x9d is a frequency at which the reproduced signal amplitude is approximately zero. On the assumption that a laser light used to read data has a wavelength xcex and an objective lens used to focus the laser light on the optical disc has a numerical aperture NA, the cut off frequency is 2NA/xcex.
The reason why the spatial frequency of the tack pitch is limited to a half to two/thirds of the cut-off frequency is that signals necessary for tracking servo and track seek should have sufficient levels, respectively, for stability of the tracking servo and track seek.
More specifically, a signal indicative of a difference between outputs from two photodetectors disposed symmetrically with respect to the track center of an optical disc (so-called xe2x80x9cpush-pullxe2x80x9d signal) and a sign al indicative of a sum of the outputs from the two photodetectors (so-called xe2x80x9ccross-trackxe2x80x9d signal) are used for the tracking servo and track seek.
Referring now to FIG. 1, there is illustrated how to produce a push-pull signal and cross-track signal. As shown, the push-pull signal is produced by detecting a reflected light from an optical disc by two photodetectors A and B disposed symmetrically with respect to the track center of an optical disc and taking a difference (Axe2x88x92B) between the two outputs from the two photodetectors A and B. The cross-track signal is produced by taking a sum (A+B) of the outputs from the two photodetectors A and B.
More particularly, assume here that two photodetectors are symmetrically with respect to the track center of an optical disc to detect a reflected light from the optical disc during data write and/or read from the optical disc. On the assumption that a quantity of light detected by one of the two photodetectors is A and that detected by the other photodetector is B. A signal indicative of a difference between the quantities A and B is a push-pull signal which is expressed as A+B, while a signal indicative of a sum of the quantities A and B is a cross-track signal which is expressed as Axe2x88x92B. Assume that the push-pull signal has an amplitude C, cross-track signal has an amplitude D and the value of the cross-track signal at a mirror surface portion of the optical disc where no trains of pits are formed is Mmax. Then, the push-pull signal amplitude ratio is expressed by C/Mmax, while the cross-track signal amplitude ratio is expressed by D/Mmax.
For MD Data 2 and DVD+RW , for example,the push-pull method is adopted for the tracking servo. Namely, the push-pull signal is used for the tracking servo. For a high stability of the tracking servo, the push-pull signal amplitude ratio has to be about 0.10 or more. For the track seek, cross-track signal is used for the traverse count. The cross-track amplitude ratio has to be about 0.05 or more. Further, in case data has been prerecorded as a train of pits on the optical disc, the pit modulation of the shortest pit has to be about 0.08 or more for normal reading of the data.
Thus, in MD data2 and DVD+RW, the spatial frequency of the track pitch is limited to a range of a half to two/thirds of the cut-off frequency for the push-pull signal amplitude ratio to be 0.10 or more, cross-track signal amplitude ratio to be 0.05 or more and for the pit modulation of the shortest pit to be 0.08 or more.
For CD and MD, the three-spot method is adopted for the tracking servo. Namely, the cross-track signal is used for the tracking servo. For a high stability of the tracking servo, the cross-track signal amplitude ratio has to be about 0.10 or more. For the track seek, the push-pull signal is used for the traverse count. For a stable track seek, the push-pull signal amplitude ratio has to be about 0.05 or more. Further, in case data has been pre-recorded as a train of pits on the optical disc, the pit modulation of the shortest pit should be about 0.08 or more for normal readings of the data.
Thus, in CD and MD, the spatial frequency of the track pitch is limited to within a range of a half to two/thirds of the cut-off frequency for the cross-track signal amplitude ratio to be 0.10 or more, push-pull signal amplitude ratio to be 0.05 or more and for the pit modulation of the shortest pit to be 0.08 or more.
However, the optical recording media are required to have a higher recording density. Namely, the optical discs are required to write data with a higher recording density. For a higher recording density of the optical recording media, the track pitch should be made smaller, for example. However, the conventional optical recording media are disadvantageous in that if the track pitch is made too smaller, signals necessary for the tracking servo and track seek cannot be produced to have sufficient level, respectively, so that the tracking servo and track, seek cannot be done stably.
Assume that a laser light used in reading data has a wavelength xcex of about 650 nm and an objective lens used has a numerical aperture NA of about 0.52. Then, in a conventional optical disc adapted for a tacking servo by the push-pull method, when it has a track pitch of 0.95 xcexcm, the push-pull signal amplitude ratio will be about 0.14, which assures a sufficient signal amplitude, so that the tracking servo can be effected stably. However, if the track pitch is 0.70 xcexcm, the push-pull signal amplitude ratio is about 0.03, which will not assure any sufficient signal amplitude, so that no stable tracking servo can be done. In addition, if data is pre-recorded as a train of pits on the optical disc, the track pitch of 0.70 xcexcm will not provide any sufficient pit modulation.
Similarly, in a conventional optical disc adapted for a tracking servo by the three-spot method, when it has a track pitch of 0.95 xcexcm, the cross-track signal amplitude ratio will be about 0.14, which assures a sufficient signal amplitude, so that the tracking servo can be effected stably. However, if the track pitch is 0.70 xcexcm, the cross-track signal amplitude ratio is about 0.02, which will not assure any sufficient signal amplitude, so that no stable tracking servo can be done. In addition, if data is pre-recorded as a train of pits on the optical disc, the track pitch of 0.70 xcexcm will not-provide any sufficient pit modulation.
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing an optical recording medium having recording tracks formed with a very small pitch, adapted for stable tracking servo and track seek as well as for a sufficient pit modulation, and thus capable of recording data with a high density.
The present invention has another object to provide a master for use to produce such an optical recording medium.
The present invention has a still another object to provide an optical recording/reproducing apparatus adapted to write and/or read data to and/or from such an optical recording medium.
The above object can be attained by providing an optical recording medium having a train,of pits formed along a recording track thereof and to and/or from which data is written and/or read by focusing thereon a light having a predetermined wavelength;
the train of pits being formed from first and second pit trains adjacent to each other, and the pits in one of the pit trains being different in depth from those in the other pit train; and
the first and second pit trains being formed to meet following relations (1) and (2) or (3) and (4) on the assumption that:
the refractive index of a material extending from the light incident surface of the optical recording medium to a surface of the optical recording medium on which the pit trains are formed is n;
the wavelength of a light used to write and/or read data to and/from the optical recording medium is xcex;
the depth of the pits in the first train is x;
the depth of the pits in the second train is y; the phase depth of the first pit train expressed by xxc3x97n/xcex is X;
the phase depth of the second pit train expressed by yxc3x97n/xcex is Y; and
K, L, M and N are arbitrary integers, respectively:
Yxe2x89xa70.5M+073.0411xe2x88x921098.4983(Xxe2x88x920.5K)+6584.7191(Xxe2x88x920.5K)2xe2x88x9219632.4312(Xxe2x88x920.5K)3+29119.8871(Xxe2x88x920.5K)4xe2x88x9217190.8276(Xxe2x88x920.5K)5xe2x80x83xe2x80x83(1)
Yxe2x89xa60.5Mxe2x88x9227.1270+307.9548(Xxe2x88x920.5K)xe2x88x921283.3732(Xxe2x88x920.5K)2+2358.2052(Xxe2x88x920.5K)3 xe2x88x921620.1442(Xxe2x88x920.5K)4xe2x80x83xe2x80x83(2)
Yxe2x89xa70.5Nxe2x88x92301.2370+2943.8278(Xxe2x88x920.5L)xe2x88x9210617.5544(Xxe2x88x920.5L) 2+16767.2625(Xxe2x88x920.5L)3xe2x88x929779.5969(Xxe2x88x920.5L)4xe2x80x83xe2x80x83(3)
Yxe2x89xa60.5N+10822.3214xe2x88x92136377.6645(Xxe2x88x920.5L)+686724.6250(Xxe2x88x920.5L)2 xe2x88x921727199.1853(Xxe2x88x920.5L)3+2169848.4081(Xxe2x88x920.5L)4 xe2x88x921089274.1768(Xxe2x88x920.5L)5xe2x80x83xe2x80x83(4)
In the above optical recording medium, since the first and second pit trains different in pit depth from each other are formed to meet the relations (1) and (2) or (3) and (4), signals necessary for the tracking servo and track seek are be provided at sufficient levels, respectively, even with the track pitch made small. This optical recording medium will be referred to as xe2x80x9cfirst optical recording mediumxe2x80x9d hereinunder for the convenience of the illustration and description of the present invention.
Also, the above object can be attained by providing a master for use to produce an optical recording medium having a train of pits formed along a recording track thereof and to and/or from which data is written and/or read by focusing thereon a light having a predetermined wavelength, the master having formed thereon:
concavity-convexity patterns for the pit trains of pits, formed for first and second ones of them to be adjacent to each other; and
the first and second pit train patterns being formed to meet following relations (5) and (6) or (7) and (8) on the assumption that:
the refractive index of a material extending from the light incident surface of the optical recording medium to a surface of the optical recording medium on which the pit trains are formed is n;
the wavelength of a light used to write and/or read data to and/from the optical recording medium is xcex;
the depth of the pits in the first train is xxe2x80x2;
the depth of the pits in the second train is yxe2x80x2;
the phase depth of the first pit train expressed by xxc3x97n/xcex is Xxe2x80x2;
the phase depth of the second pit train expressed by yxc3x97n/xcex is Yxe2x80x2; and
K, L, M and N are arbitrary integers, respectively:
Yxe2x80x2xe2x89xa70.5M+73.411xe2x88x921098.4983(Xxe2x80x2xe2x88x920.5K)+6584.7191(Xxe2x80x2xe2x88x920.5K)2xe2x88x9219632.4312(Xxe2x80x2xe2x88x920.5K)3+29119.8871(Xxe2x80x2xe2x88x920.5K)417190.8276(Xxe2x80x2xe2x88x920.5K)5xe2x80x83xe2x80x83(5)
Yxe2x80x2xe2x89xa60.5Mxe2x88x9227.1270+307.9548(Xxe2x80x2xe2x88x920.5K)xe2x88x921283.3732(Xxe2x80x2xe2x88x920.5K)2+2358.2052(Xxe2x80x2xe2x88x920.5K)3xe2x88x921620.1442(Xxe2x80x2xe2x88x920.5K)4xe2x80x83xe2x80x83(6)
Yxe2x80x2xe2x89xa70.5Nxe2x88x92301.2370+2943.8278(Xxe2x80x2xe2x88x920.5L)xe2x88x9210617.5544(Xxe2x80x2xe2x88x920.5L)2+16767.2625(Xxe2x80x2xe2x88x920.5L)3xe2x88x929779.5969(Xxe2x80x2xe2x88x920.5L)4xe2x80x83xe2x80x83(7)
Yxe2x80x2xe2x89xa60.5N+10822.3214xe2x88x92136377.6645(Xxe2x80x2xe2x88x920.5L)+686724 6250(Xxe2x80x2xe2x88x920.5L)2xe2x88x921727199.1853(Xxe2x80x2xe2x88x920.5L)3+2169848.4081(Xxe2x80x2xe2x88x920.5L)4xe2x88x921089274.1768(Xxe2x80x2xe2x88x920.5L)5xe2x80x83xe2x80x83(8)
In the above master, since the first and second pit train patterns are formed to meet the relations (5) and (6) or (7) and (8), the master can be used to produce the optical recording medium having formed thereon the first and second pit trains which meet the relations (1) and (2) or (3) and (4). Therefore, signals necessary for the tracking servo and track seek are be provided at sufficient levels, respectively, even with the track pitch made small. This master will be referred to as xe2x80x9cfirst maserxe2x80x9d hereinafter for the convenience of the illustration and description of the present invention.
The above object can be attained also by providing an optical recording/reproducing apparatus adapted to write and/or read data to and/or from an optical recording medium having a train of pits formed along a recording track thereof and, to and/or from which data is written and/or read by focusing thereon a light having a predetermined wavelength; the train of pits being formed from first and second pit trains adjacent to each other, and the pits in one of the pit trains being different in depth from those in the other pit train, the apparatus comprising:
two photodetectors disposed symmetrically with respect to the track center of the optical recording medium;
a quantity of light reflected from the optical recording medium, detected by one of the two photodetectors being assumed to be A while that detected by the other photodetector is assumed to be B, a difference signal (Axe2x88x92B) indicative of a difference between the quantities A and B being used for a tracking servo to have a light spot track a recording track.
In this optical recording/reproducing apparatus, a sum signal (A+B) indicative of a sum of the quantities A and B is used for a track seek to move a light spot to a desired recording track. Note that the first optical recoding medium can preferably be used in this first optical recording/reproducing apparatus.
The first optical recording/reproducing apparatus is adapted to play the optical recording medium having formed thereon the pit trains different in pit depth from each other. With this optical recording medium, signals necessary for the tracking servo and track seek can be provided at sufficient levels, respectively, even with the track pitch made small. That is, playing an optical recording medium having the adjacent pit trains different pit depth from each other, the optical recording/reproducing apparatus according to the present invention can use the above-mentioned difference signal or push-pull signal to effect a tracking servo stably and use the above-mentioned sum signal or cross-track signal to effect a stable track seek, even with the small track pitch.
Also, the above object can be attained by providing an optical recording medium having a train of pits formed along a recording track thereof and to and/or from which data is written and/or read by focusing thereon a light having a predetermined wavelength;
the train of pits being formed from first and second pit trains adjacent to each other, and the pits in one of the pit trains being different in depth from those, in the other pit train; and
the first and second pit trains being formed to meet following relations (13) and (14) or (15) and (16) on the assumption that:
the refractive index of a material extending from the light incident surface of the optical recording medium to a surface of the optical recording medium on which the pit trains are formed is n;
the wavelength of a light used to write and/or read data to and/from the optical recording medium is xcex;
the depth of the pits in the first train is x;
the depth of the pits in the second train is y;
the phase depth of the first pit train expressed by xxc3x97n/xcex is X;
the phase depth of the second pit train expressed by yxc3x97n/xcex is Y; and
K, L, M and N are arbitrary integers, respectively:
Yxe2x89xa70.5M+35.8289xe2x88x92569.0171(Xxe2x88x920.5K)+3607.3326(Xxe2x88x920.5K)2xe2x88x9211369.4693(Xxe2x88x920.5K)3+17816.5986(Xxe2x88x920.5K)4xe2x88x9211104.0253(Xxe2x88x920.5K)5xe2x80x83xe2x80x83(13)
Yxe2x89xa60.5Mxe2x88x9212.2807+148.0165(Xxe2x88x920.5K)xe2x88x92669.8877(Xxe2x88x920.5K)2+1466.8185(Xxe2x88x920.5K)3xe2x88x921589.1663(Xxe2x88x920.5K)4703.5593(Xxe2x88x920.5K)5xe2x80x83xe2x80x83(14)
Yxe2x89xa70.5Nxe2x88x92226.5608+1670.0195(Xxe2x88x920.5L)xe2x88x924087.700(Xxe2x88x920.5L)2+3326.6228(Xxe2x88x920.5L)3xe2x80x83xe2x80x83(15)
Yxe2x89xa60.5Nxe2x88x929579.2677+92165.2641(Xxe2x88x920.5L)xe2x88x922399.1612(Xxe2x88x920.5L)2+532600.3255(Xxe2x88x920.5L)3xe2x88x92319883.9178(Xxe2x88x920.5L)4xe2x80x83xe2x80x83(16)
This optical recording medium will be referred to as xe2x80x9csecond optical recording mediumxe2x80x9d hereinafter for the convenience of the illustration and description of the present invention.
In the second optical recording medium, since the first and second pit trains different in pit depth from each other are formed to meet the relations (13) and (14) or (15) and (16), signals necessary for the tracking servo and track seek are be provided at sufficient levels, respectively, even with the track pitch made small.
The above object can be attained also by providing a master for use to produce an optical recording medium having a train of pits formed along a recording track thereof and to and/or from which data is written and/or read by focusing thereon a light having a predetermined wavelength, the master having formed thereon:
concavity-convexity patterns for the pit trains of pits, formed for first and second ones of them to be adjacent to each other; and
the first and second pit train patterns being formed to meet following relations (17) and (18) or (19) and (20) on the assumption that:
the refractive index of a material extending from the light incident surface of the optical recording medium to a surface of the optical recording medium on which the pit trains are formed is n;
the wavelength of a light used to write and/or read data to and/from the optical recording medium is xcex;
the of the pits in the first train is xxe2x80x2;
the depth of the pits in the second train is yxe2x80x2;
the phase depth of the first pit train expressed by xxe2x80x2xc3x97n/xcex is Xxe2x80x2;
the phase depth of the second pit train expressed by yxe2x80x2xc3x97n/xcex is Yxe2x80x2; and
K, L, M and N, are arbitrary integers, respectively:
xe2x80x83Yxe2x80x2xe2x89xa70.5M+35.8289xe2x88x92569.0171(Xxe2x80x2xe2x88x920.5K)+3607.3326(Xxe2x80x2xe2x88x920.5K)2xe2x88x9211369.469(Xxe2x80x2xe2x88x920.5K)3+17816.5986(Xxe2x80x2xe2x88x920.5K)4xe2x88x9211104.0253(Xxe2x80x2xe2x88x920.5K)5xe2x80x83xe2x80x83(17)
Yxe2x80x2xe2x89xa60.5Mxe2x88x9212.2807+148.0165(Xxe2x80x2xe2x88x920.5K)xe2x88x92669.8877(Xxe2x80x2xe2x88x920.5K)2+1466.8185(Xxe2x80x2xe2x88x920.5K)3xe2x88x921589.1663(Xxe2x80x2xe2x88x920.5K)4+703.5593(Xxe2x88x920.5K)5xe2x80x83xe2x80x83(18)
Yxe2x80x2xe2x89xa70.5Nxe2x88x92226.5608+1670.0195(Xxe2x80x2xe2x88x920.5L)xe2x88x924087.700(Xxe2x80x2xe2x88x920.5L)2+3326.6228(Xxe2x80x2xe2x88x920.5L)3xe2x80x83xe2x80x83(19)
Yxe2x80x2 less than 0.5Nxe2x88x929579.2677+92165.2641(Xxe2x80x2xe2x88x920.5L) xe2x88x92332399.1612(Xxe2x80x2xe2x88x920.5L)2+532600.3255(Xxe2x80x2xe2x88x920.5L) 3xe2x88x92319883.9178(Xxe2x80x2xe2x88x920.5L)4xe2x80x83xe2x80x83(20)
This master will be referred to as xe2x80x9csecond masterxe2x80x9d hereunder for the convenience of the illustration and description of the present invention.
In this second master, since the first and second pit train patterns are formed to meet the relations (17) and (18) or (19) and (20), the master can be used to produce the optical recording medium having formed thereon the first and second pit trains which meet the relations (13) and (14) or (15) and (16). Therefore, signals necessary for the tracking servo and track seek are be provided at sufficient levels, respectively, even with the track pitch made small.
Also, the above object can be attained by providing an optical recording/reproducing apparatus adapted to write and/or read data to and/or from an optical recording medium having a train of pits formed along a recording track thereof and to and/or from which data is written and/or read by focusing thereon a light having a predetermined wavelength; the train of pits being led first and second pit trains adjacent to each other, and the pits in one of the pit trains being different in depth from those in the other pit train, the apparatus comprising:
two photodetectors disposed symmetrically with respect to the track center, of the optical recording medium;
a quantity of light reflected from the optical recording medium, detected by one of the two photodetectors being assumed to be A while that detected by the other photodetector is assumed to be B, a difference signal (Axe2x88x92B) indicative of a difference between the quantities A and B being used for a track seek to move a light spot to a desired recording track.
This optical recording/reproducing apparatus will be referred to as xe2x80x9csecond optical recording/reproducing apparatusxe2x80x9d hereinafter for the convenience of the illustration and description of the present invention. In this optical recording/reproducing apparatus, a sum signal (A+B) indicative of a sum of the quantities A and B is used for a track seek to move a light spot to a desired recording track. Note that the second optical recoding medium can preferably be used in this second optical recording/reproducing apparatus.
The second optical recording/reproducing apparatus is adapted to play the optical recording medium having formed thereon the pit trains different in pit depth from each other. With this optical recording medium, signals necessary for the tracking servo and track seek can be provided at sufficient levels, respectively, even with the track pitch made small. That is, playing an optical recording medium having the adjacent pit trains different in pit depth from each other, the optical recording/reproducing apparatus according to the present invention can use the above-mentioned difference signal or push-pull signal to effect a tracking servo stably and use the above-mentioned sum signal or cross-track signal to effect a stable tack , even with the small track pitch.